Sources said the player has become frustrated by a lack of playing time following Alexis Sanchez's arrival from Arsenal in January and because negotiations over a new contract have stalled.

Bayern Munich, Juventus and Chelsea are among the clubs interested but United will not consider selling to a Premier League rival.

While Mourinho is open to selling Martial, who scored 11 goals in 45 games last season, there are concerns among club chiefs that it could come back to haunt them if the 22-year-old goes on to fulfil his undoubted potential elsewhere.

Martial has one year left on his contract and United also hold an option to extend his deal by an additional 12 months, effectively tying him down until 2020.

Mourinho sees Martial's disquiet as an opportunity to bring in another winger, sources said. He is interested in Inter Milan's Ivan Perisic and Willian at Chelsea.